1. Field of the Invention
This invention relates to a method for making 1-alkene/maleic anhydride addition polymers which contain more than an equimolar amount of maleic anhydride through the use of a proportional feed process for mixing the monomers at a reaction temperature which is at least 145.degree. C. and to the addition polymer obtained by that process.
2. Description of the Prior Art
Those skilled in the art have commonly believed that polymers of maleic anhydride and 1-alkenes only form polymers containing approximately equimolar ratios of maleic anhydride and 1-alkenes (also known as "alpha-olefins").
For example, U.S. Pat. No. 3,461,108 to Heilman et al. teaches that copolymers of maleic anhydride and an aliphatic olefin such as 1-hexene can be reacted in molar ratios of olefin to maleic anhydride varying from 0.1:1 to 100:1. However, Heilman et al. teaches that the result is a copolymer product that is essentially a chain of alternate groupings of maleic anhydride and the olefinic monomer reactants even though much higher or lower ratios of olefin to maleic anhydride than 1:1 were used. Heilman et al. teaches that the reaction temperatures to make such polymers are between 20.degree. C. and 200.degree. C., with preferred temperatures between 50.degree. C. and 120.degree. C. Examples 17 and 18 of this Heilman, et al. patent teach reacting 100 moles of maleic anhydride with 1 mole of 1-hexene at 60.degree. C. for 165 hours to obtain a large, semi-solid gummy agglomerated mass. No analysis of the resulting mass is reported in those examples. Various methods for bringing the reactants together are taught such as by mixing all of the reactants together in a batch system or by adding the olefin intermittently or continuously to the reaction pot.
Similar teachings with regard to processing, molar ratios, and the equimolar composition of the final product for polymers of maleic anhydride with other 1-alkenes are found in Hazen, et al. U.S. Pat. Nos. 3,553,177; 3,560,455; 3,560,456; and 3,560,457 and in Heilman, et al. U.S. Pat. No. 3,706,704, all of which are assigned to Gulf Research & Development Company, as is U.S. Pat. No. 3,461,108. U.S. Pat. No. 2,938,016 to Johnson (Monsanto Chemical Company) has a similar statement about equimolar nature of the final product, but Examples 34, 35 and 39 employ an initial excess of maleic anhydride and more olefin is then added during the process.
U.S. Pat. No. 4,358,573 to Verbrugge teaches that terpolymers of maleic anhydride and alpha olefins containing a small excess of maleic anhydride relative to total alpha olefin can be obtained under certain conditions such as when high initiator levels are used. Verbrugge teaches terpolymers containing up to 60 mole percent of maleic anhydride although his examples teach adding molten maleic anhydride and initiator dropwise to a flask containing solvent and alpha olefins that was heated to 160.degree. C.
U.S. Pat. No. 4,522,992 to Verbrugge contains similar teachings with regard to terpolymers containing maleic anhydride, an aromatic monoalkenyl monomer such as styrene and a 1-alkene having at least 18 carbon atoms. However, the process used is different since, in the Examples, one alkene is placed in a flask with solvent and heated to 140.degree. C. The maleic anhydride is placed in one dropping funnel and the aromatic monomer and initiator is placed in a second dropping funnel. The contents of the dropping funnels are slowly added to the heated flask over a period of time.
U.S. Pat. No. 3,178,395 to Muskat teaches use of peroxide catalysts in excess of 2% coupled with temperatures in excess of 90.degree. C. where the monomers reacted are in the molar ratio of 1:2 to 2:1 olefin to maleic anhydride to result in a product which usually has a molar ratio of substantially 1:1.
U.S. Pat. No. 2,542,542 to Lippincott et al. teaches reacting maleic anhydride with 1-alkenes at 100.degree. to 200.degree. C. using a peroxide catalyst where the presence and nature of the solvent used changed the molar ratio of maleic anhydride to 1-alkene in the product.
Contrary to accepted beliefs, U.S. Pat. No. 4,192,930 to Beck, et al. teaches that the copolymers used are preferably those comprising maleic anhydride and olefins in a molar ratio of 0.8:1 to about 1.8:1 and states that such are known in the art, yet no specific examples of the manufacture of polymers having greater than 1:1 molar ratios of maleic anhydride to olefins are given. U.S. Pat. No. 4,072,621 to Rose teaches that the ratio of maleic anhydride to vinyl alkyl ether or 1-alkenes having 1-4 carbon atoms in the polymers useful in his invention is from 2:1 to 1:2, but does not give examples showing how to make polymers containing greater than equimolar ratios of maleic anhydride.
U.S. Pat. No. 3,261,798 to Farley teaches maleic anhydride/alpha-olefin copolymers where the reactants are added in a molar ratio of 1:1 to 1:9 (maleic anhydride excess) made at 130.degree. C. to 180.degree. C. in solvent using dialkyl peroxides. Use of a solvent is said to result in inclusion of greater than stoichiometric amounts of maleic anhydride in the product such as 1:1.43. Example 1 of the Farley patent teaches adding all of the olefin mixture and one half of the initiator to the reaction vessel and then adding the remainder of the initiator and the maleic anhydride to the flask over a period of time at 140.degree.-145.degree. C. No analysis of the polymer was reported.
U.S. Pat. No. 4,083,794 to Lee, et al. teaches the use of copolymers of maleic anhydride with a monoethylenically unsaturated monomer or mixture of monomers such as ethylene or propylene as well as methyl methacrylate or styrene where the molar ratio of maleic anhydride to unsaturated monomer is from 2.5:1 to 100:1, preferably from 2.5:1 to 30:1 and more preferably, from 2.5:1 to 7:1. Examples 8 and 9 employed 2.5 moles of maleic anhydride to 1 mole of ethylene and propylene, respectively, but these examples were written in the present tense. The copolymers and their production are said to be taught in British Pat. No. 1,414,918 which teaches copolymers of various olefin monomers and maleic anhydride in the above proportions having a molecular weight of between about 300-1000, but only teaches ethylene and propylene as 1-alkenes and provides no working examples other than the same disclosure of Examples 8 and 9 of the '794 patent. The British '918 patent prefers copolymers of acrylic or methacrylic acid and their derivatives or styrene as agents to prevent boiler scale formation.
U.S. Pat. No. 3,755,264 to Testa teaches production of copolymers of acrylic acid, styrene or vinyl acetate with maleic anhydride where the copolymers contain 99 to 85 mole percent of maleic anhydride by using a large amount of free-radical initiator (at least 6% by weight) by adding the monomer incrementally to maleic anhydride at 100.degree. C. to 145.degree. C. It does not suggest using 1-alkenes in this process.
U.S. Pat. No. 3,264,272 to Rees teaches a method of making low molecular weight copolymers of maleic anhydride and alpha-olefins, preferably styrene, which are free of homopolymers of the alpha-olefin and contain an excess of the olefin. The invention involves using higher temperatures such as greater than 140.degree. C. while feeding the styrene and maleic anhydride into a reactor together dissolved in solvent.
None of the above patents appear to recognize what we have discovered with regard to making polymers of maleic anhydride and 1-alkenes that contain more than an equimolar amount of maleic anhydride, and preferably greater than 60 mole percent of maleic anhydride.